When a physical layer of a Long Term Evolution (Long Term Evolution, LTE) system is used to perform a service of direct communication between user equipments (for example, a first user equipment and a second user equipment) (Device to Device Proximity Service, D2D ProSe), the first user equipment needs to send a discovery signal to the nearby second user equipment, so that the second user equipment can recognize the nearby first user equipment according to the discovery signal and receive the discovery signal; then a process of direct communication between the first user equipment and the second user equipment is implemented, which includes, for example, a series of processes including call initiation, channel measurement, channel feedback, resource scheduling, data transmission, call completion, and the like.
In an existing D2D ProSe, for example, a data frame of an LTE time division duplex (Time Division Duplexing, TDD) system or a data frame of an LTE frequency division duplex (Frequency Division Duplexing, FDD) system may be used to transmit a D2D signal between a first user equipment and a second user equipment, where the D2D signal includes a discovery signal and a direct communication signal.
However, because the first user equipment sends a D2D signal to the second user equipment by using downlink timing of an LTE system, and the second user equipment receives a D2D signal by using uplink timing of the LTE system, when the downlink timing is different from the uplink timing, a time difference exists between a time at which the D2D signal sent by the first user equipment reaches the second user equipment and the uplink timing of the second user equipment, and the existing time difference causes interference between OFDM symbols in a data frame. As a result, the second user equipment cannot parse out the D2D signal, and performance of the D2D ProSe is affected.